The invention relates to semiconductor lasers, and more particularly to semiconductor laser diodes having a single lateral optical mode.
There is an increasing demand for high power semiconductors that operate in the fundamental spatial mode. The spatial mode can be considered to include two components, namely the transverse component, lying perpendicular to the layers forming the semiconductor junction and the lateral component, lying parallel to the junction layers. The light generated by the semiconductor laser is generally transversely confined by having cladding layers, of relatively low refractive index, on either side of the active layer, having a relatively high refractive index. Since the active layer is generally very thin, about 1 xcexcm or so, a semiconductor laser usually emits light with a fundamental transverse component. However, a semiconductor laser typically requires lateral confinement in order to operate in the fundamental lateral mode. Lateral confinement may be provided, for example, by a buried heterostructure, a ridge waveguide or other structures that produce an effective difference in refractive index between the active region and the lateral region.
The requirement of fundamental lateral mode typically requires the width of the lateral waveguide to be small. However, this restricts the power available from the device, thus limiting its use in high power applications, such as pumping fiber amplifiers. Increasing the lateral width of the waveguide results in higher power, but also permits the oscillation of lateral modes higher than the fundamental mode, particularly at high operating powers. This leads to a reduction in the focusability of the output from the laser. Where the output from the laser is focused into a fiber, the reduction in focusability leads to a reduction in fiber coupling efficiency.
Therefore, there is a requirement for a laser that can operate at high powers while maintaining a single lateral mode.
Generally, the present invention relates to a high power, single lateral mode semiconductor laser that has a waveguide with regions of different widths coupled between a tapered region. The output from the laser is taken from the wide end of the waveguide.
In one particular embodiment of the invention, a light source includes a semiconductor laser having a laterally confining optical waveguide having a highly reflecting first end and a second end. The optical waveguide has a first portion extending from the first end and a second portion extending from the second end. The first and second portions are coupled by a tapered waveguide. A width of the first portion end is less than a width of the second portion. The first portion filters lateral optical modes higher than a fundamental lateral optical mode. An output is emitted from the second end of the optical waveguide.
Another embodiment of the invention is a fiber optic system, comprising a communications fiber including an excitable fiber medium, and a pump laser coupled to supply pump light to the excitable fiber medium. The pump laser includes a laterally confining optical waveguide having a highly reflecting first end and a second end. The optical waveguide has a first portion extending from the first end and a second portion extending from the second end. The first and second portions are coupled by a tapered waveguide. A width of the first portion end is less than a width of the second portion. The first portion filters lateral optical modes higher than a fundamental lateral optical mode. An output is emitted from the second end of the optical waveguide.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.